Register has a post on Hong Kong's investigate of going underground for data centers.
Hong Kong plans cavernous underground data centres
According to Amod Jayawant, director of critical environments at real estate services firm CBRE, digging a data bunker won't be easy.
“It’s a great idea – as you know underground rock formations, caves, caverns etc. maintain an even all year round cool temperature,” he told El Reg. “However, the technical side of this equation is not so pretty. It’s really a bunch of questions, the answers to which are sometimes not feasible or extremely expensive.”
These questions revolve around how to supply power and fit generators; how to vent diesel fumes and get fresh air in; how to get diesel tanks underground; and how to dehumidify the area, he explained.